In this paper the use of radar signal is proposed to collect the micro-Doppler signatures of motor vehicle vibrations. Specifically, two different measurement setups based on mmWave Multiple Input Multiple Output (MIMO) radar are employed for the experimental tests: the former employing a single-chip radar and the latter employing a multi-chip radar. The tests are performed on a car equipped with both petrol engine and methane engine. By properly processing the collected signatures, the most significant vibration frequencies associated to each engine are measured. By comparing the obtained results, the second radar demonstrates that it is possible to improve the measurement capability of the system by introducing a greater number of virtual elements in the receiver virtual array.